If this option is toggled on, the user can define the rotation center prior to rotating the model. If the button is hit, eta/DYNAFORM prints the following message in the message prompt window:
PICK A LOCATION AS THE ROTATION CENTER
The user can click anywhere in display window as the rotation center. Then, move the mouse cursor to rotate the model around the center.
If shortcut key (CTRL+ left mouse button) is used to rotate the model, the immediate location upon which the mouse cursor is placed is automatically defined as the rotate center. The model is rotated around the center.